I also like the way they look, but I think another reason you don't see them as much is that they just aren't as strong. A more solid handle material bolsters the strength of the tang. Even when the leather is new, it has a lot more flex than wood/micarta/bone etc. I'm not saying I'll never make one, but I'd be more inclined to use a few as spacers, then finish the handle off in a rigid material.